Scientists have produced four baby monkeys who each have three biological parents.
They used an IVF procedure designed to stop the spread of incurable inherited diseases.
Scientists believe the breakthrough could lead to the first genetically engineered children within a few years
It has provoked an ethical storm, however. Critics say it is a step towards an era of hybrid children and warn that it erodes the sanctity of life.
The technique is intended to help women who carry genetic diseases. It involves transferring healthy DNA from the mother’s egg cell into an egg donated by another woman.
Children conceived by the technique would inherit DNA from three sources - their mother, the donor and their father.
The American team who produced the macaque monkeys - named Mito, Tracker, Spindler and Spindy - say the technique could be used to eradicate potentially fatal forms of inherited epilepsy, blindness and heart disease.